Posted
by
Soulskillon Friday April 04, 2014 @02:25PM
from the i'll-volunteer-everyone-in-california dept.

Hugh Pickens DOT Com writes: "The nearest star systems — such as our nearest neighbor, Proxima Centauri, which is 4.2 light-years from home — are so far away, reaching them would require a generational starship. Entire generations of people would be born, live, and die before the ship reached its destination. This brings up the question of how many people you need to send on a hypothetical interstellar mission to sustain sufficient genetic diversity. Anthropologist Cameron Smith has calculated how many people would be required to maintain genetic diversity and secure the success of the endeavor. William Gardner-O'Kearney helped Smith build the MATLAB simulations to calculate how many different scenarios would play out during interstellar travel and ran some simulations specially to show why the success of an interstellar mission depends crucially on the starting population size. Gardner-O'Kearny calculated each population's possible trajectory over 300 years, or 30 generations. Because there are a lot of random variables to consider, he calculated the trajectory of each population 10 times, then averaged the results.

A population of 150 people, proposed by John Moore in 2002, is not nearly high enough to maintain genetic variation. Over many generations, inbreeding leads to the loss of more than 80 percent of the original diversity found within the hypothetical gene. A population of 500 people would not be sufficient either, Smith says. "Five hundred people picked at random today from the human population would not probably represent all of human genetic diversity . . . If you're going to seed a planet for its entire future, you want to have as much genetic diversity as possible, because that diversity is your insurance policy for adaptation to new conditions." A starting population of 40,000 people maintains 100 percent of its variation, while the 10,000-person scenario stays relatively stable too. So, Smith concludes that a number between 10,000 and 40,000 is a pretty safe bet when it comes to preserving genetic variation. Luckily, tens of thousands of pioneers wouldn't have to be housed all in one starship. Spreading people out among multiple ships also spreads out the risk. Modular ships could dock together for trade and social gatherings, but travel separately so that disaster for one wouldn't spell disaster for all. 'With 10,000,' Smith says, 'you can set off with good amount of human genetic diversity, survive even a bad disease sweep, and arrive in numbers, perhaps, and diversity sufficient to make a good go at Humanity 2.0.'"

"By the time we have the tech to build a starship we can just ship out as many embryos as we can fit in a freezer. Job done."

Not quite.

The 18 years we spend now may be excessive but even figuring adulthood at 15 those embryos do not just magically hatch out as viable colonists. So while this might be a reasonable side-project to help a little, it's far from "job done."

Another way to cut down on the requirements is to deliberately pick the colonists based on genetics rather than assume a 'random' sample. I am normally against any sort of pseudo-racial quota system on principle, but in this one narrow case it would have a direct and clear justification. If instead of assuming random participants, you assume participants deliberately picked to be as genetically distant from each other as possible, you should be able to reduce the population requirements quite significantly.

If instead of assuming random participants, you assume participants deliberately picked to be as genetically distant from each other as possible, you should be able to reduce the population requirements quite significantly.

Or just store all the genome diffs of all of humanity on a one terabyte SD card. Then when you need some genetic diversity, just synthesize the DNA strand and splice it into the appropriate chromosome. Then there is need for an extra freezer. You might want to take along an extra backup of the SD card.

... just synthesize the DNA strand and splice it into the appropriate chromosome.

Are we anywhere near that kind of technology yet?

Yes, we can synthesize DNA, and insert it into genomes. We also have terabyte SD cards. They are expensive, but the cost should drop by the time the multi-generational starships are ready to launch.

The human genome has about 4 billion base pairs. Each pair can be encoded in two bits (there are four different monomers). Since each eight bit byte can encode four base pairs, the entire human genome can fit in one GB. But each for each additional genome, we only need to encode the diffs. Humans are 99.9% the same [wikipedia.org] so a typical diff would be about 0.1% of 1GB, or 1MB. But even that understates the compression possible, because that 0.1% is not random. People tend to diverge from other people in "chunks" that are shared across many other people. So a typical person's genome could probably be stored in about 100KB. Properly compressed, a terabyte SD card could contain the genomes of ten million people.

I think the point was something more like, "We don't need to worry about genetic diversity if we can just pack embryos." That way, you can staff the spaceship with an appropriate number of people for making the trip and establishing a colony, and then use the embryos once you hit the point of needing genetic diversity.

Or pack eggs and sperm, mix as needed. Or just biological samples that can be cloned. Or hell, if we're getting really sci-fi here, maybe we can perform direct genetic manipulation by that

" I think the point was something more like, "We don't need to worry about genetic diversity if we can just pack embryos." That way, you can staff the spaceship with an appropriate number of people for making the trip and establishing a colony, and then use the embryos once you hit the point of needing genetic diversity. "Whoosh.

Let's try again. Say you take 150 people to run the ship, and figure to get your 10k population level with these embryos after they arrive. You can incubate them (if you brought the

" I think the point was something more like, "We don't need to worry about genetic diversity if we can just pack embryos." That way, you can staff the spaceship with an appropriate number of people for making the trip and establishing a colony, and then use the embryos once you hit the point of needing genetic diversity. "

Whoosh.

Let's try again. Say you take 150 people to run the ship, and figure to get your 10k population level with these embryos after they arrive. You can incubate them (if you brought the equipment) but then you get 10k squalling infants and only 150 people to provide food shelter education and attention for them for the next decade plus before they start carrying their own weight. It just doesnt work that way.

You don't grow the embryos all at once - you do it over several generations, so first you grow enough childcare providers and educators to handle the next generation. So you have 200 people to run the ship, then grow 200 children (so each ship staff is responsible for raising one child, though there will be dedicated childcare centers, etc to help out) to act as dedicated childcare providers/educators and 15 years later when they are ready to do their jobs, you can raise 800 more (4 per dedicated childcare

Don't be a dick. I was exactly pointing out what you alluded to later in your post:

The best you could do would be to keep a slow but steady trickle of incubations going, no more than the current number of adult colonists can handle in addition to their natural offspring...

They're talking about the genetic diversity as a long-term issue for sustainable colonization of a planet. A controlled trickle of additional diversity over time would probably give you exactly what you need. The fact that you'll be living in "extreme frontier living" probably means that you don't want to start of with an enormous population right away. So again, you could (and probably should) focus on figuring out how m

What's extreme frontier living for people arriving by starship? They're going to have massive power sources and fully automated manufacturing facilities capable of making anything (including more automated manufacturing facilities), because starships need such power sources and probably such manufacturing facilities.

"By the time we have the tech to build a starship we can just ship out as many embryos as we can fit in a freezer. Job done."

Not quite.

The 18 years we spend now may be excessive but even figuring adulthood at 15 those embryos do not just magically hatch out as viable colonists. So while this might be a reasonable side-project to help a little, it's far from "job done."

I would assume that they embryos would be inseminated and implanted into the human colonists, so people wouldn't have to follow a chart to decide who they can procreate with, all procreation comes from the stored embryos hand picked to ensure genetic diversity. Though I don't know how long embryos could be stored in a freezer.

Another way to cut down on the requirements is to deliberately pick the colonists based on genetics rather than assume a 'random' sample. I am normally against any sort of pseudo-racial quota system on principle, but in this one narrow case it would have a direct and clear justification. If instead of assuming random participants, you assume participants deliberately picked to be as genetically distant from each other as possible, you should be able to reduce the population requirements quite significantly.

How significantly? The frozen embryo plan seems to make the population more manageable -- They could keep a constant 100 (or 1000 or whatever) colonists on board for the first 250 year

By the time we have the tech to build a starship we can just ship out as many embryos as we can fit in a freezer. Job done.

We might, depending on how Team AI makes out, need to have a nonzero number of humans either as an active population or in some flavor of cryo, to gestate and socialize Generation 0; but even with the technology we have today, right now, the idea of sending an entire human if you just need some genetic diversity seems slightly insane.

Especially for sperm, where you don't even have the difficulties associated with egg collection(by no means a pleasant process) or the mediocre success rates associated with

With using a smaller population and using stored embryos, we could simulate genetic diversity for the duration of the trip. So the next question is how big an adult crew you will need to keep the genetic population if you have some setup as a backup.

I'm skeptical of those numbers anyway: There have been times [wikipedia.org] where the total number of humans was less than 40k with some speculation that there were as few as 2k for a while. That discounts, say, early settles to regions that then became the native people. How large a group traveled through the Bering Strait to the Americas? With current knowledge, we could screen the initial people for genetic diseases and organize breeding programs to maintain diversity, so we could probably be successful with even less.

Anyways, the ability to freeze bits (sperm, eggs, embryos) already exists and the projected lifetime of sperm at least would easily cover the journey plus the formative years. Heck, it's probably a better solution than legions of people even from a purely genetic perspective as you could probably better control radiation damage.

So that means genetics aren't really going to be as important as:*) Builders - You aren't going to grandma's. You'll need able-bodies people to build you colony. Robots can help, but it's still going to require a decent crew. Even if you don't maintain this size group throughout the journey, you'll need it when you arrive, meaning the ship needs to have facilities for them to grow up in.*) Parents - You need to keep people alive to teach new people what being people is. Books and other media will help, but you need a decent assortment to give an understanding of 'society' and prevent one bad egg over the 300 years from spoiling the bunch.*) Society - Kinda tied to the last point, but you can't just have 10 people playing poker for 300 years. You need some ability to socialize, have friends, create, consume, etc.

I'd side with the anthropologist on this one: 150ish, a small village worth. Genetics are basically a solved problem and pretty much a footnote on the laundry list of problems that colonizing would face. Heck we don't even know if Proxima Centauri has a planet!

You're thinking small. By the time we have the tech even to build a credible slowboat, we'll have the tech to just ship the basic human genetic code plus a library of admissible variations and we'll assemble the humans at the far end from scratch, robotically. That way we don't need to worry about hundreds of years of radiation exposure (frozen or not, damaged DNA is damaged DNA) or the slow but unstoppable dehydration and diffusion out of the embryos. We can also ship the genetic code plus variation lib

The point of exploring the stars will never be to "reduce the surplus population". That's not likely to be a real problem in any case.

The point is to broaden humanity's knowledge, perspective, and diversity. To make us, collectively, more than we are now.

But the stars are out of reach without some revolutionary new understanding of physics. The energy budget for interstellar travel is insane, assuming we want to get somewhere within a generation. It's far beyond workable fusion power needed for a starship: either some sort of warp drive, or antimatter fuel and a rocket with near-light speed exhaust.

The nice thing is, relativity means you can travel ridiculously long distances in subjective time and with an energy budget not much worse than going 100 light years. Humanity on Earth, not to mention the Sun, may be long gone when you get there, but you can visit other galaxies if only you had a magical power source.

The energy budget for interstellar travel is insane, assuming we want to get somewhere within a generation.

Why should we need to get there in a generation? A 500 year trip could be made at 1% of c. Which means only 6000-odd km/s (got to have a maneuvering reserve) of delta-V, which is not especially difficult to achieve once we have a workable fusion drive.

Use a reasonably sized asteroid as your starship, and go - so it'll be your umpteen-great grandchildren who will arrive - no biggy.

Sure, that's only ~5 TWH/ton. By comparison, the US as a whole consumes on average about 1 TW. If you spent 100 years of that time boosting, you'd need about ~5 MW of power generation (including 100 years of fuel) per ton of spaceship. So we're back to "revolution in physics".

Send a sperm bank and a handful of (very dedicated) women, deter first cousins or closer from breeding, population remains low it doesn't expand until the ship nears it's destination, it then expands at a predetermined rate to provide the workforce needed to construct the colony upon arrival.

Some sort of magic shield would be nice as well. There is mostly nothing but space in space; but there's nothing like colliding with it at the thick end of the speed of light to teach you that 'mostly nothing' and 'nothing' differ slightly.

to be honest what is the use of this? Why do we want embryos on an other planet. Having to much people on earth won't be solved by sending embryos to other planet... As long as they can't send a large group of people in a short time to an other planet. This whole traveling to other planets is useless...

Redundancy. Overpopulation is not the reason -- that's a self-correcting problem.

Having all of humanity stuck on a single planet in a single solar system leaves mankind open to extinction from a rare planet ending or even a more rare solar system ending event. Though we probably need to get out of the Galaxy for true redundancy. I don't think there's any way to avoid the eventual end of the universe, whether its ends in a big freeze or big crunch...But we have a bit of time before that happens, so it can be left for future generations, as long as we don't end up killing ourselves or depleting our resources before we can get off the planet.

And who says, we didn't already do this? Send out lots of ships to other planets. After that we got some water problems, like Noah's story. After that only a few people survived, started to multiply and created a new civilization. Those people we send out there, are now living happily. And yes, there comes a bunch of embryo's again....

I'm pretty sure the fossil record is complete enough to rule out modern humans suddenly popping up from seeded embryos.

Humans are interesting animals.We are still 80% dependent on fossil fuels for our energy needs and have no clue what we could use at this scale when they're depleted.But let's worry about what could happen to the sun in 5 billion years!

Humans are interesting animals.We are still 80% dependent on fossil fuels for our energy needs and have no clue what we could use at this scale when they're depleted.

The other interesting thing about humans is that they are all independent beings, so some of them can be thinking about and working on one thing, and others can be working on something completely different... at the same time!

But let's worry about what could happen to the sun in 5 billion years!

I think the death of the sun is the least of our worries -- it seems far more likely that humans will have been wiped off the planet by an asteroid collision. And that could happen at any time with little warning - even if we see it coming a decade in advance, there's very little we ca

The sad thing continues to be postings how staying safe, playing video games, and watching football games continues to be more "fulfilling" than the real adventure you describe./sigh

One problem is that society has become increasingly risk adverse in many ways - I doubt the Apollo program would pass a NASA safety review today. And we waste billions of dollars to ostensibly prevent a terrorist attack against an airliner, yet we have no problem facing a far higher risk of dying when we drive to the airport.

No method of space travel that seems remotely feasible would dent an overpopulation problem. Suppose we wanted to reduce population growth by 0.1%/year by shipping people out; that's 7 million people per year, something like twenty thousand a day, or one every four or five seconds. Unless we develop something like cheap and practical teleportation over interstellar distances, this isn't going to happen. With any reasonably imaginable tech, it's going to be really expensive to get them into Earth orbit.

We're going to explore the Galaxy because it's out there, to learn things, and to make it much harder for the species to be destroyed.

As it happens, those methods are big on drama and small on results. By way of example: here's Europe [wolframalpha.com], in millions, from the mid 19th century to more or less the present.

Notice the two tiny little dips around 1914 and 1939, and the effect (bugger all) if you take the longer view of, say, 1900-1975? That's two world wars, few genocides, and massive devastation of infrastructure. Not much population control per unit unpleasantness...(and if you think of this period as not especially 'sin'-pocked, maybe you would get along well with a certain old testament deity.)

Famine and plague are similarly good for painful, short-term, die-offs that just leave a bit of room below environmental carrying capacity that ends up being filled out by a new crop of poor fuckers within a generation or two. Disposable income and contraception, though? Now that will crater your birthrate more effectively, if less dramatically, than saturation bombing.

What we really need is to bring a complete biosystem with us, enough species diversity to successfully colonize the planet with food producing plants that help maintain some semblence of stability in the O2 / CO2 levels and the temperature.

I'm not sure, the female colonists — born and raised in space, BTW — will all agree to inseminate themselves with the thawed sperm of strangers instead of following the instinct to conceive in the hot embrace of their lovers.

Some of them might, but it is a risk, that the idea will be rejected en masse...

Perhaps, we'll develop incubators capable of replacing women's wombs — but even then there might be a problem with such kids being discriminated against i

You don't have to send men at all in the first round. This gives at least until the colonist women dub the first generation of male children fuckable where if they're going to be pregnant, it's going to be embryos.

The other thing is, the entire sperm bank doesn't have to be spent in generation 1. With an inbreeding taboo and geneology, you could go several generations before you found yourself backed into a corner.

Don't need males for the first 30--35 years. Use pre-selected (female) embryos for the first 35 years.... then allow males to enter the general population. (Wow, just realized: for hundreds of years, no one will have seen a male!)

"I'm not sure, the female colonists — born and raised in space, BTW — will all agree to inseminate themselves with the thawed sperm of strangers instead of following the instinct to conceive in the hot embrace of their lovers. "

That's sort of the point. The 'lovers' stay at home, you take only females on the flight an reproduce only females during the flight. Only on arrival you'd raise men.

If it's just genetic diversity you're worried about, why send the people themselves? It seems to me that sending that many people would be a massive over-expenditure of resources. Why not send much more manageable number of people to run the ship and build the initial settlement along with preserved genetic material for a massively larger population. Breed, predominantly, through artificial insemination for the initial generations until you are back to having the desired diversity in the actual living population.

All this discussion about genetic diversity. What about the knowledge? What sort of information would we need to pass on through those generations to have them actually able to recolonize and succeed? How do we pass on advancements as they get further and further away and the time lapse gets worse and worse?

I'd imagine if we had a bunch of inbreeds to the point we reach Idiocracy and no one knows how to hold a spoon, much less how to construct a building, there would be bigger problems to overcome.

A lot of people (not us Slashdotters, of course) have the misconception that other solar systems are right next door to ours. So I always illustrate it like this: The fastest spacecrafts we've ever built take about 9 years or so to go from Earth to Pluto. At that rate, they would take about 120,000 years to reach the next closest solar system. I also saw a great illustration once using a quarter (coin), to represent our solar system, and the next solar system being something like two football fields away.

The fastest spacecrafts we've ever built take about 9 years or so to go from Earth to Pluto. At that rate, they would take about 120,000 years to reach the next closest solar system.

That's only because they spend most of this time without acceleration — in free fall. Once we find a way to continuously accelerate the ship even at the comfortable 1g, the 9 years shrinks to a couple of months (you accelerate for half the distance and then turn around and begin decelerating for the rest)...

The fastest spacecrafts we've ever built take about 9 years or so to go from Earth to Pluto. At that rate, they would take about 120,000 years to reach the next closest solar system.

That's only because they spend most of this time without acceleration — in free fall. Once we find a way to continuously accelerate the ship even at the comfortable 1g, the 9 years shrinks to a couple of months (you accelerate for half the distance and then turn around and begin decelerating for the rest)...

Question:

Instead of turning around at the halfway point and using the same thrust to decelerate, would it be possible to, theoretically, initiate an explosion in front of the craft, equal in yield to the amount of thrust used to achieve whatever speed your craft is at when you need to start accelerating? Kind of like the old police trick of pulling in front of a speeding car and using the police cruiser to slow it (but with a BOOM instead of brakes, obviously).

But then you have to carry enough fuel to accelerate the fuel you need to decelerate. Unless you have a reactionless engine, in which case the ghost of Isaac Newton would like a word with you about his third law...

Even with that, the nearest star is around 6,400 times as far from us as Pluto is. If you could shrink the travel time down to 2 months to go to Pluto, you'd still be talking hundreds of years to get to the nearest star.

"Space is big. Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space." == Seems appropriate here.

Its unlikely that they would send people like that, or that they would survive on a planet after adapting to 120,000 years worth of space travel.

They would construct a spacecraft that can accelerate at around 10 m/s^2 over hundreds of years, midway though the journey they flip it around and decelerate at the same pace. If the target planet is higher or lower gravity, they can ramp up or down acceleration to aclimant people to the change.

Five hundred people picked at random today from the human population would not probably represent all of human genetic diversity . . . If you're going to seed a planet for its entire future, you want to have as much genetic diversity as possible, because that diversity is your insurance policy for adaptation to new conditions

when it comes to preserving genetic variation

Except that's not the goal.If you're talking about colonizing another star system (presumably this is way the fuck after we colonize mars, the moon, IO, Titan, Venus, Murcury, and whatever else we feel like) then little things like genetic diversity upon reaching the target are of little concern.

No, you care about GETTING THERE with enough wits about you that you can continue to function, and set up something to expand your capabilities.The fight is not to keep the diversity we see on earth circa 2000, but rather the fight is against inbreeding from making everyone retarded to the point where they can no longer function.

Once you get there, and establish colonies, food supply, and your ecosphere can expand past the mothership, you can breed like rabbits and let nature take it's course to overcome whatever detrimental effects that being cooped up in a closed space for 30 generations might have had.

Or every generation could be a fucking clone while on the way there. Seriously, this is colonizing ANOTHER SOLAR SYSTEM. This is WAY OUT THERE. It's science fiction. Just what the hell were you planning of propelling this ship with for 30 years?

Hell, taking the long view, just spreading ANY form of sustainable life is a viable goal for this sort of project. At this scale, "humans" are transient things.

30. Thirty generations. And they're worried about inbreeding. Because of the population cap that a closed environment like a colony ship would impose.

As for needing diversity when you get there. No. That's not quite right. Once there you can develop diversity. Or, you WILL develop diversity unless everyone stays in the same place for some reason. Do you think "staying healthy" is the same as "staying homo sapian"? Because that ain't gonna happen. Place humans on different planets and I guarantee that we wi

I wonder if they are taking into account whether the people involved will want to procreate with each other. Just because there are enough bodies to maintain adequate diversity, doesn't mean everyone will happily pair up to make that happen. That is a much more difficult calculation. That being said, if you have a short list of potential breeding partners, some people will become less picky.

To me, the question is not really how many people, but how many earthworms, and in general plants, bugs, birds, animals, etc.? At present, we really have no idea what is needed, nor in how much variation within each species, but I suspect the real answer will always be "more that we think."

Well that becomes a very interesting question when you consider the idea of a completely self-sustaining spaceship. Imagine you had to create a spaceship could contain an entire ecosystem ideal for human habitation, surviving indefinitely. What would that look like? How would you keep all the different populations alive, but also checking population growth? And let's ideally imagine that it could keep itself in check without too much intervention.

How many species would we need? I don't think that question has an answer, because of the somewhat vague definition of what a species is. Culex pipiens, restuans, and quinquifasciatus are very similar mosquito species that readily hybridize to form completely viable offspring; would you need *all three of them*? You might; these are important disease vectors, both human (Saint Louis and Japanese Encephalitis) and animal (dog heartworm), and its quite possible that some genetic populations don't spread ce

On a vaguely related note: Assume you send N ships on this voyage. Do you send N copies of the same ship, and hope the design has no fatal flaw (while acknowledging the advantages of parts redundancy) . Or do you send N different designs in the hope that diversity of design is overall more reliable?

On a vaguely related note: Assume you send N ships on this voyage. Do you send N copies of the same ship, and hope the design has no fatal flaw (while acknowledging the advantages of parts redundancy) . Or do you send N different designs in the hope that diversity of design is overall more reliable?

You send N ships and let them breed of course. It may cause an occasional bumpy ride, and sure some of the younger ships will keep asking "Are we there YET?!?!". Then there will be the rebellious phase where the ships pierce their deflector dishes, get decals plastered over their aft thrusters, and deviate to the Orion Nebula because "that's what all the cool ships are doing". But in the end, you'll end up with enough mature and responsible ships to keep things going.

While you would clearly be getting volunteers for the start of this task, there is an ethical dillema as far as future generations. Just because parents / grandparents / great-grandparents were totally OK living their entire lives in what would be a fairly finite space, it doesn't mean some members of a future generation wouldn't consider it torture. I guess it might be hard for me to see things from their eyes since they would be born into it, but I'm thinking that after I got to learn some history and see some videos / pictures of Earth, I'd be pretty unhappy stuck on a spaceship forever. I wonder how many would refuse to breed and do the same to their offspring (which would screw up the "diversity", or decide to turn back, or just go stark-raving-mad and murder someone or everyone (destroy the ship), and then your genetic diversity is REALLY screwed.

Have you seen how fucked up the world is now? Yet we keep having children...

Worse, if you're religious, you acknowledge that if your kid decides to live his life wrong, he may well end up tortured forever in hell. So you're bringing in to the world a soul that you love, that might be forever tormented. And yet since you lived right, you're in heaven. How exactly am I supposed to enjoy heaven when my son is burning in hell?

If you send too few people out then production won't be high enough in the beginning. You need to send a fair few billion out to at least the first few star systems so that the population can grow, then once the colony is establish, you need to ship people back to maintain production levels on the home world. This is basic stuff people.

Early human population dwindled to as few as 2000 individuals with most living in isolated pockets of a few hundred. Given enough time the population and genetic variability rebounded. Colonization of other worlds is most definitely a long-term project and while a bigger sample might give you better chances its probably possible with far fewer individuals.

That was my first thought too, that this has already happened. Current theories place the human population minimum at around 10K so maybe this guy is right. http://en.wikipedia.org/wiki/T... [wikipedia.org]

Look at the Pacific and check how big populations on remote islands have to be to stay healthy (Easter Island for example). From that, 10.000 looks much more realistic than 500.

But there is another problem which has not been addressed: Keeping or even raising the technological level of this population. Even a population of 10.000 will be very small in this respect. Evidence: The early inhabitants of Tasman Island arrived by boat and knew how to make arrows and such, but their descendants lost all that kno

Assuming the closest is even viable, which it probably isn't, 4.2 Light Years = 39735067984839.36 Kilometers. The fastest thing (only thing) man has sent out of our solar system is Voyager 1, which at its current speed, if it was pointed in the right direction would take about 73,775 years to reach the target. Considering you probably don't want to run into it at that speed, you will have to accelerate and decelerate. Which it doesn't have the fuel for (never mind its RTG energy source is only good for 60-80 years), but even if it did would roughly double the time to reach the intended target to about 147,550 years. OK well that's not quite true, it would only add an insignificant amount of time because not a lot of time was actually spent to accelerate in the first place. However in the example below where you do not coast for tens of thousands of years, and accelerate til the midway point and then immediately start to decelerate it would double whatever you speed VS distance is anyway.

Sure you could accelerate and decelerate much harder than that to get there much faster, approaching whatever value of c is currently capable at launch. However by any measure, unless some magic energy source and method of propulsion is devised, the required energy at least at today's standards would require carting around the hydrogen energy mass of our sun for the trip. Some other methods of insitu material gathering such as ram scoops picking up interstellar dust are as likely as the fiction, as again unless some dark matter type thing which is everywhere (presumably) is harnessed, the amount of mass available is pretty low, space as it turns out is pretty damn empty.

Not to mention the weirdness of relative time as one approaches c on a ship compared to Earth, as while it may take less than the 75k years voyager would, here on Earth many more years will have elapsed. As to how many, I have no idea, that is beyond my math calculating ability (as is generally most of what I have currently written I am sure will be pointed out).

Never mind trying to maintain a ship, machinery, technology, or even a society that long!

More likely colonization will involve self replicating and regenerating robotic ship carrying a genetic payload and an informational database (likely with a terra forming mission proceeding it). Which would be more like favorable seeding for similar evolution and life to occur, than an actual "colony". Then again, that would also require pretty adaptive programming and AI, which would likely mean we would probably be fertilizer for our robotic overlords petunia plants.

So I guess I am saying as a thought experiment it is sort of interesting, but at this point (or any really foreseeable point in our future), it is all a bit far fetched by even the loosest standards.

Sure, if you *cap* the population at 150 during transit, and don't allow multiple pairings within the same generation of course you're going to kill the genetic diversity.

However, if instead of a generational ship we were talking about hibernation until arrival, 150 is enough to begin a genetically viable colony. How do you avoid the risk of inbreeding? Simple: no cap on the number of children, but no full siblings allowed. Encourage as many different genetic pairings as possible.

" The recent African origin theory for humans would predict that in Africa there exists a great deal more diversity than elsewhere, and that diversity should decrease the further from Africa a population is sampled. Long and Kittles show that indeed, African populations contain about 100% of human genetic diversity, whereas in populations outside of Africa diversity is much reduced"

This is a naive estimate—typical of wide-eyed wanderlust—looking at one tiny piece of the problem.

I'd say a population of about a million is necessary to maintain working contact with human technological culture, and pass this working contact on to the next generation. There's a bit of a gap between a Wikipedia article on metallurgy and a guy who has practised the profession for several decades.

In anthropology, often when a smaller population contracts major technologies are lost, not because t

1) It ignores the possibility of storing DNA. In vials. 40,000 sperm samples and the equipment to store it frozen can fit in less space than 10 people. Not to mention a nice electronic record can hold the DNA of millions yet fit in my pocket.

2) It assumes that transportation will take 100's of years. Within 100 years, our space technology should be able to deliver 10 people 4 light years away (one way trip), in no more than 50 years travel time. That is two generations.

3) There is no reason to select people 'randomly', we can easily intentionally select people non-randomly, making sure that they have minimal DNA in common. Often 'random' ensures that weird coincidences happen.

4) The Toba theory claims that humans had a bottleneck of 3,000-10,000 individuals. 10,000 is a HIGH end, not a low end of what we need.

Generation ships are impossible** for humans, which will likely cause our extinction.

Although technically and logically, it is not an insurmountable problem. You need a small crew, 6 or 7 women per generation. A high number of frozen male and double that many frozen female embryos (which we will assume are viable forever, though we don't know).

All crew members birth one daughter. If one is not successful, one crew member births 2 daufghters.

They are raised to be the next generation of crew.

Many generations later, strict population control (through gender homogeny) 6 or 7 women will land on target planet (or more likely orbit it)

Exploratory team of males/females are raised during the last "transport" generation, then they are sent on a lander as a pilot program, meanwhile another generation of female crew is needed.

If pilot program is successful and either farming is not needed (if gatherer lifestyle is possible on destination) either send more landers, or land the craft and begin large scale birth-rate increases, with every female birthing 6 or more embryos as health allows.

While using up the rest of the embryos (which will be an exponential thing) Ease humanity into a reproductive lifestyle, as it will be culturally foreign to them.

**This requires so much space culture cooperation and "unethical" planning that humans would never do it. We are more likely to spend all of our natural resources to make a GIANT space ship that crashes and kills thousands of people instead, because of the "religion/culture" problem, which is unsolvable.

Sending meat bags into space is not very practical at all. It's more likely that we'll develop nano-factories and the capability of offloading intelligence into machines. Then we can just create intelligent space drones that replicate themselves as they go along and thus populate the galaxy.

This is actually one of the reasons why some think there is no extraterrestial life advanced enough to pull this off, as we would have noticed it by now. The reasoning behind this is that any society that has such capabilities more than likely destroyed itself before being able to reach this state. Of course, we might just be the first in our universe to pull this off, but don't count on it.

Ten women for every man and they woman..."I hasten to add that since each man will be required to do prodigious... service along these lines, the women will have to be selected for their sexual characteristics which will have to be of a highly stimulating nature. "

Why not just allow for inbreeding and do continuous genetic testing on all embryos generated, terminating those that will turn into West Virginians?

Why not just allow inbreeding? It's how we fucking colonized Earth. Genetic diversity isn't something to strive for, it's simply a result of a population surviving long enough in different circumstances (from diet to weather to disease). Absolutely none of the issues our current genetic diversity handles will be an issue for a colonization program. All people chosen will be screened appropriately so we'll know they're all decently healthy, and all potential catastrophic problems will be completely unlik